The present invention relates to a pneumatic tire which exhibits an excellent performance on ice and snow.
Conventionally, a pneumatic tire which is provided with a plurality of blocks on a tread surface, wherein the blocks are defined by main grooves formed in the tire circumferential direction, lug grooves formed in the tire transverse direction and the like has existed. By providing blocks on a tread surface in such a manner, a pneumatic tire ensures favorable braking and traction force, steering stability and the like.
Also, improvement in performance on ice and snow and a wet property has been attempted by providing sipes in the blocks to increase an edge length and to increase gripping force.
Further, under the tread surface of the pneumatic tire formed in this way, reinforcing layers in which a number of steel cords are provided parallel to each other are laminated in order to strengthen stiffness of the tread.
In the pneumatic tire structured as described above, the contact patch area side of each block is divided by sipes into a plurality of small blocks. When the tire rotates, each of the small blocks tends to lean backward due to the frictional force exerted between itself and the road surface. When the degree of leaning becomes large, a contact patch area area of the contact patch area decreases, so that there is a possibility that the performance on ice and snow may deteriorate.
However, the small blocks are compressed in a height direction (the direction oriented toward the tire axis from the contact patch area) by ground contact pressure from the contact patch area and expand in a cross direction (the direction perpendicular to the height direction). As a result, the small blocks abut the adjacent small blocks across the sipes, so that leaning thereof is suppressed to a certain extent.
However, if the sipes are formed straight in the sipe depth direction, deformation of the small blocks due to ground contact is not capable enough of causing the small blocks to contact the adjacent small blocks with sufficient force. Accordingly, leaning suppression is weak and thus it can hardly be said that contact patch area area of the contact patch area is sufficiently ensured.
Further, a plurality of steel cords disposed in each of the reinforcing layers are provided parallel to each other and inclined at a predetermined angle with respect to the tire circumferential direction. Thus, there has been a problem in that when a vehicle on which the pneumatic tires are actually fitted is driven, the steel cords provided in the reinforcing layer closest to the tread surface side lean toward the tire circumferential direction, thereby generating a force to restore the tire distorted by ground contact pressure to the original shape (Self Alignment Torque, referred to as SAT hereinafter).
In view of the above-described circumstances, an object of the present invention is to provide a pneumatic tire which exhibits an excellent performance on ice and snow by suppressing leaning of blocks having sipes, and which suppresses SAT.
A first aspect of the present invention is a pneumatic tire comprising: a plurality of reinforcing layers in which cords, which are inclined at a predetermined angle with respect to a tire circumferential direction, are provided parallel to each other; a tread provided on a top of the reinforcing layers which are laminated; and a block-shaped land portion having a sipe, the block-shaped land portion being defined on a tread surface by main grooves formed in the tire circumferential direction and by lug grooves formed in a direction intersecting the main grooves; wherein the sipe is shaped so as to be twisted around a first central axis of twisting extending in a tire radial direction in the block-shaped land portion and a second central axis of twisting extending substantially in a tire transverse direction, a position P1 of the first central axis of twisting in a region between one end surface of the block-shaped land portion and another end surface in the tire transverse direction and a position P2 of the second central axis of twisting in a region between a contact patch area and a bottom of the sipe in the tire radial direction being within ranges satisfying the following relational expressions:
0.2 Wxe2x89xa6P1xe2x89xa60.8 W
0.2 Fxe2x89xa6P2xe2x89xa60.6 F
wherein P1, P2 represent the position of the first and second central axes of twisting respectively; W represents a distance from the one end surface to the other end surface of the block-shaped land portion in the tire transverse direction; and F represents a distance from the contact patch area to the bottom of the sipe in the tire radial direction.
In the first aspect of the invention, since the sipe is shaped so as to be twisted around the first central axis of twisting extending in the tire radial direction and the second central axis of twisting extending substantially in the tire transverse direction, the block-shaped land portion is compressed in a height direction due to ground contact pressure and expands in a cross direction, and as a result, small blocks divided by the sipe abut each other. Moreover, since the sipe is twisted, the small blocks abut each other not only due to a force exerted in the tire circumferential direction (the tire rotation direction), but also due to forces exerted from other directions. Further, since the small blocks perform a rotational motion due to ground contact pressure, the adjacent small blocks abut each other with a strong force.
Moreover, the position P1 of the first central axis of twisting is within the range of 0.2 Wxe2x89xa6P1xe2x89xa60.8 W with respect to a distance W (referred to as width W hereinafter) from one end surface to the other end surface of the block-shaped land portion in the tire transverse direction, and the position P2 of the second central axis of twisting is within the range of 0.2 Fxe2x89xa6P2xe2x89xa60.6 F with respect to a distance F (referred to as sipe depth F hereinafter) from the contact patch area to the bottom of the sipe in the tire radial direction, and because of this positioning, stiffness of the small blocks increases further and leaning thereof is suppressed compared to structures with positioning in which the first central axis of twisting and the second central axis of twisting are located at positions not within the above-mentioned ranges (see FIG. 24 and FIG. 25).
In this way, the small blocks abut each other with a strong force due to the sipes being formed with a twist, and stiffness of the small blocks can be increased by positioning the first central axis of twisting and the second central axis of twisting of the sipe within the predetermined ranges. Accordingly, leaning can be suppressed with certainty. As a result, a contact patch area area on the contact patch area of the small blocks increases, and performance on ice and snow improves.
Further, when ground contact pressure acts on the contact patch area of the block-shaped land portion, the block-shaped land portion is compressed in the height direction, so that each of the small blocks, while guided by the sipe, rotationally deforms in a direction in which the sipe is further twisted. Due to this deformation, an SAT (a torque for restoring the small blocks to the original shapes) exerted in a direction opposite to the twisting direction of the sipe is generated on each of the small blocks.
Thus, by forming the block-shaped land portion, in which the sipes are twisted in an appropriate direction, on the tread surface, the SAT generated by an inclination, relative to the tire circumferential direction, of the cords which form an outermost layer of the reinforcing layers is reduced. That is, the SAT due to the cords can be suppressed by the SAT generated at the block-shaped land portion.
Accordingly, a favorable steering stability on icy and snowy roads and the like can be obtained with a vehicle to which such pneumatic tires are mounted.
A second aspect is a pneumatic tire comprising: a plurality of reinforcing layers in which cords, which are inclined at a predetermined angle with respect to a tire circumferential direction, are provided parallel to each other; a tread provided on a top of the reinforcing layers which are laminated; and a block-shaped land portion having a sipe, the block-shaped land portion being defined on a tread surface by main grooves formed in the tire circumferential direction and by lug grooves formed in a direction intersecting with the main grooves; wherein the sipe is shaped so as to have a first protruding portion protruding in a first direction with respect to a virtual central plane and a second protruding portion protruding in a second direction opposite the first direction across the virtual central plane, the sipe including a surface portion exposed on a contact patch area of the block-shaped land portion and a bottom portion formed in a bottom of the sipe, the virtual central plane being twisted from the surface portion toward the bottom portion.
In the second aspect of the invention, since the sipe has a structure twisted from the surface portion toward the bottom portion, when the block-shaped land portion is compressed in a height direction due to ground contact pressure and expands in a cross direction, small blocks divided by the sipe abut each other. Moreover, since the sipe (the virtual central plane thereof) is twisted, the small blocks abut each other not only due to a force exerted in the tire circumferential direction (the tire rotation direction), but also due to a force exerted from other directions. Further, since the small blocks perform a rotational motion due to ground contact pressure, the adjacent small blocks abut each other with a strong force.
In this way, since the sipe is formed with a twist, the small blocks abut each other with a strong force, so that leaning is suppressed with certainty. As a result, a contact patch area area on the contact patch area of the small blocks increases, and the performance on ice and snow improves.
In particular, since the sipe is not only twisted, but also formed with the first protruding portion and the second protruding portion, that is, with a shape having recessed and protruding portions across the virtual central plane, the deformation of the block-shaped land portion due to ground contact pressure suffices to cause the small blocks to abut each other with a stronger force and increase contact area. Thus, leaning is suppressed further and a contact patch area area on the contact patch area increases, so that the performance on ice and snow improves even more.
Moreover, when ground contact pressure is exerted on the contact patch area of the block-shaped land portion, the block-shaped land portion is compressed in the height direction, so that each of the small blocks, while guided by the sipe, deforms in a direction in which the sipe (the virtual central plane thereof is further twisted. Due to this deformation, SAT (a torque for restoring the small blocks to their original shapes) exerted in a direction opposite to the twisting direction of the sipes is generated on each of the small blocks.
Thus, by forming the block-shaped land portion, in which the sipes are twisted in an appropriate direction, on the tread surface, the SAT generated by an inclination, relative to the tire circumferential direction, of cords which form an outermost layer of the reinforcing layers is reduced. That is, the SAT due to the cords can be suppressed by the SAT generated at the block-shaped land portion.
Accordingly, a favorable steering stability on icy and snowy roads and the like can be obtained with a vehicle to which such pneumatic tires are mounted.
A third aspect of the invention is a pneumatic tire according to the second aspect, wherein the vtrtual central plane is shaped so as to be twisted around a first central axis of twisting extending in the tire radial direction in the block-shaped land portion, a position P1 of the first central axis of twisting in a region between one end surface of the block-shaped land portion and the other end surface in the tire transverse direction being within a range satisfying the following relational expression:
0.2 Wxe2x89xa6P1xe2x89xa60.8 W
wherein P1 represents the position of the first central axis of twisting; and W represents a distance from one end surface to the other end surface of the block-shaped land portion in the tire transverse direction.
In the third aspect of the present invention, the sipe is formed with a shape in which the virtual central plane is twisted around the first central axis of twisting extending in the tire radial direction. In this case, since the position P1 of the first central axis of twisting is within the range of 0.2 Wxe2x89xa6P1xe2x89xa60.8 W with respect to the width W of the block-shaped land portion, stiffness increases more than in the small blocks divided by the sipe whose position P1 is not within the above-mentioned range (see FIG. 24). Thus, leaning of the small blocks is further suppressed and a contact patch area area on the contact patch area increases, so that the performance on ice and snow improves even more.
A fourth aspect of the invention is a pneumatic tire according to the second and third aspects, wherein the virtual central plane is shaped so as to be twisted around a second central axis of twisting extending substantially in the tire transverse direction in the block-shaped land portion, a position P2 of the second central axis of twisting in a region between the contact patch area and the bottom of the sipe in the tire radial direction being within a range satisfying the following relational expression:
0.2 Fxe2x89xa6P2xe2x89xa60.6 F
wherein P2 represents the position of the second central axis of twisting; and F represents a distance from the contact patch area to the bottom of the sipe in the tire radial direction.
In the fourth aspect of the invention, the sipe is formed with a shape in which the virtual central plane is twisted around the second central axis of twisting extending substantially in the tire transverse direction. In this case, since the position P2 of the second central axis of twisting is within the range of 0.2 Fxe2x89xa6P2xe2x89xa60.6 F with respect to the sipe depth F, stiffness increases more than in the small blocks divided by the sipe whose position P2 is not within the above-mentioned range (see FIG. 25). Thus, leaning of the small blocks is further suppressed and a contact patch area area on the contact patch area increases, so that the performance on ice and snow improves even more.
A fifth aspect of the invention is a pneumatic tire comprising: a plurality of reinforcing layers in which cords, which are inclined at a predetermined angle with respect to a tire circumferential direction, are provided parallel to each other; a tread provided on a top of the reinforcing layers which are laminated; and a block-shaped land portion having a sipe, the block-shaped land portion being defined on a tread surface by main grooves formed in the tire circumferential direction and by lug grooves formed in a direction intersecting the main grooves; wherein the sipe is shaped as a closed loop which is connected with neither the main groove nor the lug groove, the sipe including a surface portion exposed on a contact patch area of the block-shaped land portion and a bottom portion formed in a bottom of the sipe, the sipe being twisted from the surface portion toward the bottom portion.
In the fifth aspect of the invention, since the sipe is structured so as to be twisted from the surface portion toward the bottom portion, when the block-shaped land portion is compressed in a height direction due to ground contact pressure and expands in a cross direction, small blocks divided by the sipe abut each other. Moreover, since the sipe which is formed in the shape of a closed loop is twisted, the small blocks divided by the sipe abut each other not only due to a force exerted in the tire circumferential direction (the tire rotation direction), but also due to forces exerted from other directions. Further, since the small blocks perform a rotational motion due to ground contact pressure, the adjacent small blocks abut each other with a strong force.
In this way, since the sipe is formed with a twist, the small blocks abut each other with a strong force, so that leaning is suppressed with certainty. As a result, a contact patch area area on the contact patch area of the small blocks increases, and a performance on ice and snow improves.
Moreover, when ground contact pressure is exerted on the contact patch area of the block-shaped land portion, the block-shaped land portion is compressed in the height direction, so that the small blocks, while guided by the sipe, deform in a direction in which the sipe is further twisted. Due to this deformation, an SAT (a torque for restoring the small blocks to their original shape) exerted in a direction opposite to the twisting direction of the small blocks is generated on the small blocks.
Thus, by forming the block-shaped land portion, in which the sipes are twisted in an appropriate direction, on the tread surface, an SAT, generated by an inclination, with respect to the tire circumferential direction, of cords which form an outermost layer of the reinforcing layers is reduced. That is, the SAT due to the cords can be suppressed by the SAT generated at the block-shaped land portion.
Accordingly, a favorable steering stability on icy and snowy roads and the like can be obtained with a vehicle to which such pneumatic tires are mounted.
A sixth aspect of the invention is a pneumatic tire according to any of the first through fifth aspects, wherein the block-shaped land portion is twisted from the contact patch area toward the bottom portion.
In the sixth aspect of the invention, since not only the sipe but also the block-shaped land portion is twisted, a force exerted on the block-shaped land portion in the rotation direction due to ground contact pressure increases. Accordingly, in the block-shaped land portion, a force which causes the adjacent small blocks to abut each other, or an SAT of the small blocks (a torque for restoring the small blocks to their original shapes) increases further, thereby further increasing steering stability of the pneumatic tire.
A seventh aspect of the invention is a pneumatic tire according to the sixth aspect, wherein a direction of twisting of the block-shaped land portion is the same as a direction of twisting of the sipe twisted from the contact patch area toward the bottom of the sipe.
In the seventh aspect of the invention, since the twist direction of the sipe twisted from the contact patch area toward the bottom of the sipe and the twist direction of the block-shaped land portion are the same, the direction of the rotation of the small blocks caused by the sipe due to ground contact pressure and the direction of the rotation of the block-shaped land portion caused by the twist of the block-shaped land portion coincide. Accordingly, an SAT (a torque for restoring the block to the original shape) generated in the block-shaped land portion increases further, thereby further facilitating suppression of the SAT generated by the cords. As a result, steering stability improves even more.
An eighth aspect of the invention is a pneumatic tire according to the sixth aspect, wherein a direction of twisting of the block-shaped land portion is opposite to a direction of twisting of the sipe from the contact patch area toward the bottom of the sipe.
In the eighth aspect of the invention, since the twist direction of the block-shaped land portion and the twist direction of the sipe twisted from the contact patch area toward the bottom of the sipe are opposite, the direction of the rotation of the block-shaped land portion caused by the twist of the block-shaped land portion and the direction of the rotation of the small blocks caused by the twist of the sipe are opposite. Therefore, the small blocks may be brought into contact with each other with a strong force. As a result, leaning of the small blocks is suppressed still further and the performance on ice and snow improves.